The present invention concerns high-voltage windings and more particularly windings of this type that can be used as dry transformer high-voltage windings.
High-voltage windings for such applications must be able to withstand voltages in the range 5 kV to 36 kV.
Solid insulation transformers or dry transformers are known per se in which the windings are coated with heat-setting insulative materials and which have sizeable airgaps assuring an insulation function between windings and between windings and the electrical earth, which increase their overall size, their mass and consequently their cost.
To overcome this problem some manufacturers use surface metallisation of the windings to reduce the overall size of the equipment.
However, this technique has the drawback of being costly and difficult to implement.
Currently there are two major families of dry transformers. Coated transformers and impregnated transformers. The methods of manufacturing these devices are certainly different, but the insulating materials used have the common features of being heat-setting and of requiring polymerisation at raised temperature, leading to high manufacturing cost.
The invention aims to reduce the aforementioned drawbacks of dry insulation devices by creating a high-voltage winding which combines performance at least as good as that of dry insulating arrangements known per se with a low manufacturing cost and enhanced operational safety.
It therefore consists in a high-voltage winding comprising a winding of conductive wire coated with an insulative sheath characterised in that said winding is coated with a high-voltage insulative thermoplastics resin and in that it further comprises a potential fixing electroconductive surface layer of a thermoplastics resin compatible with the thermoplastics resin of the insulative coating deposited on that coating.
In accordance with other features of the invention:
the winding includes a lateral strip of insulative thermoplastics resin compatible with the insulative material of the coating of the winding, of increased thickness relative thereto and covering the connecting conductors of the winding and orifices are formed in the insulative coating and in the covering strip for the ends of the connecting conductors so that they can be connected to other components;
the resin of the insulative coating is selected from the group comprising 6xe2x80x946 polyamides, 6-polyamides, 4,6-polyamides, 12,12 polyamides, 6-12 polyamides, polyamides containing aromatic monomers, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, liquid crystal polymers, polycyclohexane dimethylol terephthalate, copolyether esters, polyphenylene sulphide, polyacylics, polypropylene, polyethylene, polyacetals, polymethylpentene, polyether imides, polycarbonates, polysulphones, polyethersulphones, polyphenylene oxides, polystyrene, styrene copolymers, mixtures and grafted copolymers of styrene and rubber and mixtures of the above substances;
the thermoplastics resin of the insulative coating is polyethylene terephthalate;
the polyethylene terephthalate is charged with glass fibres;
the thickness of the thermoplastics resin of the insulative coating is in the range 3 mm to 50 mm;
the electroconductive thermoplastics resin of the potential fixing layer contains a charge of carbon;
the winding-constitutes the high-voltage winding of a dry transformer.
The invention also consists in a method of producing a high-voltage winding, characterised in that it consists in:
winding a conductive wire coated with an electro-insulative sheath to form a hollow cylindrical winding;
in a first mould, moulding a first coating of the winding in an electrically insulative thermoplastics resin to obtain a layer of electrically insulative thermoplastics resin of sufficient thickness for the winding to be insulated from the exterior, and
in a second mould, moulding onto the winding complete with its electrically insulative thermoplastics resin layer a second coating in the form of a potential fixing electroconductive thermoplastics resin layer.
In accordance with other features of the invention, the coating phase in the first mould consists in:
placing the winding in the cavity of a mould having an inlet, a vent orifice and rods for supporting an object inside the mould;
moving the rods into contact with the winding to support it in the cavity;
injecting the electrically insulative thermoplastics resin into the mould through its inlet;
withdrawing the rods out of the cavity when the thermoplastics resin is injected into the cavity before it sets around the rods to prevent the formation of voids in the electrically insulative thermoplastics resin;
allowing air to exit the cavity through the vent orifice when the resin fills the mould, and
continuing to inject the electrically insulative thermoplastics resin until the mould is filled to form an electrically insulative thermoplastics resin layer that is practically free of voids and of sufficient thickness for the winding to be insulated from the outside;
injection of the electrically insulative thermoplastics resin is continued until a uniform thickness of at least 3 mm is obtained on the outside and inside diameters of the winding and a uniform thickness of at least 2.5 mm is obtained at the axial ends of the winding;
the second coating with the electroconductive thermoplastics resin layer is performed by hot compression moulding.